Is it ever proper to end questions with だ? For instance:
I have been told it was correct and incorrect by many parties, but I've always learned to just raise the ending intonation to denote an inquiry.
Interrogative phrases ending in だ (with the exception of dialects) are used to demand information.
As in the following:
か is the usual way to ask a question, but it is quite acceptable to drop the か if you use a proper "questioning" intonation. You could just say "好き?" if you used the proper intonation.
... 誰だ？ -- could be a regular question.
... 誰だ？ -- could be a [rhetorical question]. See Is a sentence ending with 誰だ but without か a question?
どんな食べ物が好きだ？ -- is typical of an adult speaking to a child.
Kind-of like (in English) : [Do you like this cake?] --vs.-- [You like this cake?]
[Is this good?] --vs.-- [This is good?]